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Title: Cell Membrane Structure - Permeability of the lipid bilayer cell membranes in a Purple Cabbage
Date: December 9, 2019
Aim: To determine the effects of different concentrations of ethanol on the permeability of the lipid bilayer cell membranes in a purple cabbage.
Apparatus and : 5 boiling test tubes, boiling test tube rack, Purple cabbage, marker, Materials masking tape, knife, distilled water, measuring cylinder (100cm^3 ), ethanol concentrations (10%, 30%, 50% and 70%), 5 beakers, pipette dropper, ruler, pencil, 5 chromatography papers, 6 petri- dishes
Method: The apparatus were cleaned and prepared. The boiling test tubes were labelled with their respective concentrations of ethanol (10%, 30%, 50%, 70%) and an additional boiling test tube was labelled distilled water ; this was the control. 20 cm^3 of each solution was measured and was poured into their corresponding boiling test tubes. A knife was used to shred the cabbage into small fragments. The shredded cabbage was placed onto petri- dishes and 10g of the shredded cabbage was weighed on the electrical balance. The same amount of shredded cabbage (10g) was placed into each boiling test tubes. The contents in the boiling test tubes were left for a total of thirty minutes. The colour shades of each boiling test tubes were observed and recorded in tables presented in the results. After the thirty minutes, 5 chromatography papers were obtained to proceed with the section of the lab. A horizontal line 1.5 cm was drawn from the base of each chromatography papers. Each chromatography paper was labelled with an alcohol concentration as well
as one for distilled water. Five beakers were filled with small amounts of water. A pipette dropper was used to take up a small amount of each solution, and one drop of each solution was placed on the middle of the horizontal line on each chromatography paper. The chromatography papers were secured onto their petri- dishes and were allowed to hang vertically. The beakers were covered with the petri- dishes so that the chromatography papers touched the water slightly. The different shades of each ethanol concentration on the chromatography papers were observed. When the solvent reached within 1 cm of the top of the paper, the chromatography papers were quickly removed, and the solvent front was marked. The length of the coloured pigment for each chromatography paper was measured and a note of the colour intensity for each of them were recorded.
NB: For the Ranking of colour intensity in the table the smaller the number the darker the shade of purple.
Pictures Showing the Results from the Experiment
Figure were seen for the different 1: In the picture above the different shades of purple concentrations of ethanol after 30 minutes. From the left going to the right: Distilled water, 10%, 30%, 50% and 70% ethanol solutions.
Figure 2: chromatography paper In the picture above the for the 70 % ethanol solution was seen to have anthocyanin in alkaline pH after the experiment. dark blue pigment of
Figure chromatography 3 : In the picture above paper for the 50 % ethanol the solution was seen to have a slightly dark blue pigment of anthocyanin in alkaline pH after the experiment.
Figure 4 paper for the: : In the picture above the chromatography 3 0 % ethanol solution was seen to have a light the experiment. blue pigment of anthocyanin in alkaline pH after
Figure 5: chromatography In the picture above paper for the the 1 0 % ethanol solution was seen to have a very pale blue pigment of anthocyanin in alkaline pH after the experiment.
Figure 6: paper for In the picture above the distilled water was the chromatography seen to have a no blue pigment of anthocyanin in alkaline pH after the experiment.
membrane would be destroyed more with a strong ethanol concentration because it is a strong fat solvent and would help dissolve large amounts of fats contained in the cell membrane hence, the Purple Cabbage cells released more purple pigment which contributed to the darker purple colour. On the other hand, the 10% ethanol solution was weaker in concentration and therefore, it would dissolve only a small amount of fats in the cell membrane making it a weak fat solvent. Hence, less purple pigment would be released from the Purple Cabbage cells which contributed the light purple colour. The 70% and 50% were seen to have darker purple colour when compared to the 10% and 30 % and distilled water as can be seen in Figure 1 above. However, the 70 % ethanol concentration was seen to have a darker purple colour when compared to the 50% ethanol concentration. This was because the lipid bilayer cell membrane would be destroyed more with a strong ethanol concentration because it is a strong fat solvent and would help dissolve large amounts of fats contained in the cell membrane hence, the Purple Cabbage cells released more purple pigment which contributed to the darker purple colour. The 50% ethanol solution was weaker in concentration and therefore, it would dissolve only a small amount of fats in the cell membrane making it a weak fat solvent. Hence less purple pigment would be released from the Purple Cabbage cells which contributed a lighter purple colour.
There was no distinct purple colour in the distilled water which indicates that water does not affect the lipid bilayer cell membrane because of its polar nature. Polar substances such as water cannot dissolve non- polar substances such as lipids because they do not form an attraction therefore, the water and the lipid in the cell membrane did not react and the cell membrane remained intact.
In the chromatography section of the experiment, the length of the pigment was measured. The anthocyanin pigment changes colour in different pH; when the water was allowed to travel vertically up the chromatography paper the pigment colour changed from
purple to blue. This was because in alkaline conditions the purple pigment changes to blue. This explained why the researchers saw a blue streak of pigment instead of an expected purple streak.
For the ethanol concentrations 10% and 30% the 10% ethanol concentration had a longer length (5.5 cm) of blue pigment (anthocyanin) and a paler shade of blue pigment than the 30% ethanol solution. The reason for this was because in the 10% ethanol solution less anthocyanin was present which meant that there were less anthocyanin molecules that travelled up the chromatography paper which made the ascent of the pigment easier and it allowed it to travel farther than the pigments in the 30% ethanol solution. The 30% ethanol solution contained more pigment, so it was harder for the molecules to travel up the chromatography paper hence it had a shorter pigment length (5.0 cm). The 30% ethanol solution had a darker shade of blue pigment than the 10% ethanol solution because of the large amounts of anthocyanin released from the Purple Cabbage cells. The 10% ethanol solution had a lighter shade of blue pigment because of the small amounts of anthocyanin released from Purple Cabbage cells. For the ethanol solutions 50% and 70% ethanol solutions, the 50% ethanol solution had a longer length (8.2 cm) of blue pigment (anthocyanin) and a slightly dark shade of blue pigment than the 70% ethanol solution.The reason for this was because in the 50% ethanol solution less anthocyanin was present which meant that there were less anthocyanin molecules that travelled up the chromatography paper which made the ascent of the pigment easier and it allowed it to travel farther than the pigments in the 70% ethanol solution. The 70% ethanol solution contained more pigment, so it was harder for the molecules to travel up the chromatography paper hence it had a shorter pigment length (7.0 cm). However, the 70% ethanol solution had a darker shade of blue pigment than the 50% ethanol solution because of the large amounts of anthocyanin released from the Purple Cabbage cells .The 50% ethanol solution had a slightly dark shade of blue
Limitations and Sources of Error: Limitation : The colour intensity (colour of pigment) was hard to discern because the different shades of purple were so close. This hindered the researchers’ accuracy in the judgment of the colour intensity of the pigment.
Source of error : Not all of the shredded cabbage was used in the experiment because some of it was left behind when the researchers attempted to place it into the respective test tubes. Also, some of the shredded cabbage got stuck to the sides of the inner test tube and did not properly react with the ethanol because the boiling test tube was small.
Reflection : Living Purple cabbage cells are excellent models for some simple experiments involving cellular membranes because it has similar features to that of the cell membranes in humans. The Purple cabbage cell permeability experiment, using ethanol, was a perfect example of how ethanol affects the cell membranes in the human body when consumed. The cell membranes in the human bodyare made up primarily of phospholipids and proteins which contribute to its selectively permeable nature. The function and permeability of the cell membranes dependon its intact structure. When destroyed, the permeability of the cell
membrane is disrupted causing cellular contents to leak out. Certain chemicals such as fat solvents (ethanol) dissolve the phospholipids, leading to damage of the membrane and therefore increased permeability.
This explains why alcohol can be easily absorbed in the human body which can lead to the death of the organism. The phospholipid bilayer is amphipathic, so the polar heads face the polar solvents (i.e. water) and the nonpolar tails are hydrophobic. Alcohol is also amphipathic (non- polar and polar properties) so the alcohol molecules have no problem dissolving the lipids (phospholipids and cholesterol) that make up the cell membrane. The alcohol molecules then penetrate the cytoplasm and destroy the inner structure of the cell molecules and of the cytoplasm’s proteins. This process is known as denaturation and the enzymes‘coagulation leads to a loss of cellular activity and, finally, to the cell’s death which lead to the organism’s death. This is why it is not unusual for alcoholics to die after constant abuse of alcoholin a short period of time.
This experiment allowed the researchers to fully understand and grasp the lipid bilayer cell membrane structure and how this structure relates to its function of separating and organizing chemicals and reactions within cells by allowing selective passage of materials across their boundaries. Also, the researchers also comprehended how other substances other than water can travel across the cell membrane, one substance was alcohol. Alcohol is amphipathic so it can easily dissolve the amphipathic phospholipid and travel through the cell membrane.
This experiment could be improved if a spectrometer/colorimeter was available in the school laboratory. The spectrometer would give the researchers a better judgement of the shade of purple pigment leaked from the Purple cabbage and would give more accurate results. Also, with the spectrometer more quantitative results can be obtained since the
